Filament spot tester



Oct. 31, 1933.

H. H. MILLAR ET AL I 1,932,633

FILAMENT SPOT TESTER Filed April 22, 1932 3 Sheets-Sheet l H. H. MILLAR ET AL FILAMENT SPOT TESTER Oct. 31, 1933. 1,932,633

3 Sheets-Sheet 2 Filed April 22, 1932 OC- 31, 1933- H. H. NULLA/R ET A1.

FILAMENT SPOT TESTER Filed April 22, 1932 3 Sheets-Sheet 5 t www A my@ UNITED STATES 1,932,633 PATENT OFFICE FILAMENT SPOT TESTER Harold H. Millar, Flushing, N. Y., and Robert Pash, Cranford, N. J., assignors to Electrical Testing Laboratories, New York, N. Y., a corporation of New York Application April 22, 1932. Serial No. 606,884

11 Claims.

The present invention relates to a novel method and apparatus for testing current-conducting wires or filaments such as are used for a Variety of purposes in light-producing and thermal devices, With reference to detection of spots or vportions of increased resistance.

Spots may be due to localized reduction in the cross-section of the wire, or due to localized contamination or non-homogeneity of the wire. Whatever may be their nature, they are essentially portions of higher resistance, and

when a current is caused to fiow through a Wire,

of the character mentioned, having a spot thereon, the latter heats up more quickly than the other portions of lower resistance, because it is supplied with greater energy by reason of its increased resistance (the current remaining the same throughout the lament), and, in the case of a spot of the character of a reduced cross-section of the wire, because it requires less heat to raise its temperature by reason of its reduced mass. Due to the fact that the resistance of the colder portions has not increased to its operating value, it often happens that the temperature of the spot is raised at the start 4to a point greatly surpassing the normal operating temperature of the lament.- However, if the spot is not too long, its temperature will lower, a fraction of a second after initial passage ofthecurrent, in general to approximately the operating temperature, or the temperature of the entire filament made substantially uniform by conduction of heat along said filament. Nevertheless, continuous operation of the spot at a somewhat higher temperature than the remaining body of the wire will in time deteriorate the wire at the spot, with the result that its life is appreciably shortened. Also, successive inrushes of current and consequent initial ment of even slight deviation from the normal` resistance of the lament. It is thus desirable to test filaments with reference to possible spots thereon. Spot testing not only enables the manufacturer ci the appliances to reject those articles which -would be certain to have a limited of spots on filaments or Wires with extreme precision and speed. I

In accordance with the invention, the filament is flashed by causing a current of predetermined strength to flow through the filament for a predetermined small period of time, to permit the spot or spots, if present on the filament, to become lighted and to be therefore rendered visible to the eye by contrast With the colder or darker portions of the filament. It should be observed that, under ordinary circumstances when passing a current through a filament and permitting its flow to be permanent, a spot is in general not visible to the eye upon inrush of current. This is because the increase in temperature of the filament as a whole is in itself so sudden as to make it impossible for the eye to detect differences in temperature set up at any instant along the filament. However, a flash is visible to the eye, even if vof very short duration, and this method of detecting spots in filaments bypassage of a current therethrough is only made possible by interrupting the current after a predetermined period of time, i. e. before the entire filament heats up to its final temperature. The flashing period must be short for obvious reasons. But, a fine filament requires a shorter period of flashing than a heavy filament, and short spots require shorter ashing periods than long spots. However, the flashing period is dependent on the current caused to pass through the filament or the voltage to which it is subjected, i. e. the shorter the iiashing period used for a given filament, the higher the voltage required., In view of the above, it is desirable to use as long a period of 'flashing as is compatible with the distinct appearance of any spot, and this same flashing period may be used for testing filaments of various sizes and spots 'of Various lengths thereon, by properly varying or adjusting the voltage supplied to the filaments.

vTo obtain the best results, an apparatus embodying this principle of spot detection should possess the following features. It should be sensitive, that is, spots of even a faint degree should be made to appear clearly. It should give uniform results, that is, make the same spot on a lament always give the same appearance when iiashed under the same voltage. This last feature involves the question of accurate timing of the flash. The apparatus should also be such that, when a number of flashing machines arel built, they should give exactly the same fiashingl period and identical results obtained for a given fllament.

A more. specific object of :"the invention is to .e

provide an apparatus for flashing filaments having the features above mentioned and enabling accurate detection of spots in filaments of various sizes.

The initial current through a cold filament is many times the normal operating current (in tungsten lamps probably over 10 times as high). Thus, since the current is interrupted with the major portion of the filament still unheated to its operating temperature, the excessive sparking occurring at the circuit-breaking contacts, unless eliminated, would soon wear them down and render the apparatus unfit for service. This would be particularly true for tests on heavy duty lamps, as "150 or 1000 watt lamps or lamps drawing even greater currents than the latter, especially if these are tested with the same flashing period as for small lamps, which would require a flashing voltage of perhaps twice the rated voltage.

An important object of the present invention is to provide circuit-controlling means for nterrupting the alternating current flowing in the filament circuit at a zero point of the alternating current wave, i. e. when the instantaneous current value is zero. By making use of such means inthe flashing of filaments,` sparking upon interruption of the current therethrough is substantially eliminated.

Further objects and advantages of the invention will appear in the following description taken in connection with the accompanying drawings in which Figs. l, 2 and'3 are' plan, front and end profile views respectively of an apparatus embodying the invention; Fig. 4 is a fragmentary cross-sectional view looking from the rear of the apparatus on the plane indicated by the line iX-4X in Fig. 1; Fig. 5 is a cross-sectional vie'w as seen from the left of the apparatus on the plane indicated by the line 5 5 in Fig. 2; Fig. 6 is an enlarged fragmentary cross-sectional view taken o n the plane indicated by the line 6 --6x in Fig. 2, and illustrates the means for adjusting the position of the low-speed commutator brushes; Fig. 'I is an enlarged fragmentary cross-sectional view taken on the plane indicated by the line 7X-7X in Fig. 3, and illustrates the construction of the brush holders; Fig. 8 is an enlarged fragmentary cross-sectional view taken on the plane indicated by the line 8 8 in Fig. 2, and illustrates the clicking device or means for sounding an alarm prior to the flash through the filament under test; Fig. 9A is a schematic illustration of conducting parts of the apparatus and accessories thereof, showing the wiring connections for a test on an electric lamp;

Figs. 10 to 13, inclusive, are schematic views of the high-speed and low-speed commutators when having rotated through various angles from their positions shown in Fig. 9.

The drawings -show an apparatus for testing electric lamp filaments, which apparatus will be described as illustrating the invention in both its general and specific aspects.

Experiments have-shown a flashing period of 1/60 of a second, corresponding to one cycle of a 60 cycle alternating current wave, to be satisfactory for tests on electric lamps of various sizes, i. e. Vthis particular flashing period was found to be thelongest period permissible (for a particular range of voltages) without impairing visibility of any spot under test. period be made longer, short spots become considerably dimmed in appearance. Using this one cycle contact and a standard lighting circuit as the source, the flashing voltage may be about the rated voltage for a 400 watt lamp, below vline If this flashing voltage for small lamps and above line voltage for larger lamps. Observing that the inrush of current through a cold filament greatly surpasses the rated value, the current to be handled by the apparatus for tests on heavy filament lamps, such as 750 or 1000 watt lamps or lamps of higher wattage than the latter, would run up into a considerable value, were this one cycle contact used. It is -thus preferable to utilize a longer flashing period for large lamps and supply less voltage to their filaments. The embodiment of the invention illustrated provides two flashing periods, one a one-cycle contact and the other a three-cycle contact, the circuit being made and interrupted in either case at zero points of the wave. It is understood, however, that a flashing period of different duration and various other flashing periods may be provided, also that contact may be caused to occur at other points than at a zero point of the wave, without departing from the principle of the invention.

The flash should preferably be repeated through a lamp under test at definite intervals. Thus, in the embodiment of the invention illustrated, the flash may be caused to recur every second, with the apparatus set to provide a flash of either one cycle or three cycles duration. It is understood, however, that, by proper design of the apparatus, the flash may be caused to occur at a time interval of different duration. It should be noted that the period of time selected for repeating the flash should not be so short as to permit the filament undergoing test to heat up unduly, as this method of testing for spots by flashing the filament depends upon passage of current through the filament when cold or essentially at low temperature.

The apparatus illustrated in the drawings cornprises a rotary switching means including a high-speed commutator 1 and a low-speed commutator 2. These two commutators are driven by a synchronous motor 4 so that their respective speeds are at any instant proportional to or in synchronism with the frequency of the alternating current power supply (preferably a standard (S0-cycle lighting circuit) to which the motor is connected, said commutators operating conjoint- 1y to alternately make and break the current in the circuit in which the filament undergoing test is disposed. The filament circuit derives its flashing current from the same power source so that the commutators are also in synchronism with the voltage on the filament circuit. Thus, by proper positioning of the brushes or switching contacts on the high-speed commutator, the latter can be caused to establish and interrupt the flashing current at zero points of the A. C. wave. The low-speed commutator has two functions. It acts to permit the flashing current to be repeatedly established every second, but is so constructed as to provide a flashing current of either one cycle o1' 'three cycles, either one of which may be selected by properinanipulation of a switch 5.

The motor 4 and the switch 5 are mounted on a suitable base 6 which also carries a plug receptacle 'I to which the motor terminals or leads (not shown) are connected. Current is supplied to the motor by attaching to this base receptacle 7 a plug 9 (see Fig. 9) adapted to be connected to the power supply. Asbest illus.

trated in Fig. 4, the motor shaft 10 is connected by suitable coupling 11 to another shaft 12, which is journaled in a bearing 14 with which is associated a stuffing box 15 of any desired construction. The bearing 14 is attached to one side of a transmission housing or oil box 16 secured to the base 6. A third shaft 17, carrying a worm gear 19, located in the housing 16, is journaled in a bearing 20 attached to the other side of the housing 16. The bearing 20 is also provided with a stuffing box 21. The

shaft 12 has its inner end inserted ina recess' in the shaft 17, and these two shafts are keyed together by a pin 22. A ball thrust bearing 24 is carried on the shaft 17 and a :collar 25 is xed to the shaft 12 to prevent longitudinal displacements of said shafts. As best illustrated in Fig. 5, a counter shaft 26 -is provided, which carries a gear 27 located within the housing 16 and meshing with the worm 19. -This shaft 26 has one end journaled inthe rear wall 29 of the housing 16 and its opposite extremity projects through a bearing 30 having a stuffing box 31. A ball thrust bearing 32 is mounted on the shaft 26 between the housing wall 29 and the gear 27,

and outer displacement of the shaft 26 and gear 27 thereon is prevented by the inner wall of the bearing 30. Oil is admitted into the housing 16 through an opening having a screw plug 33.

The high-speed commutator 1 consists of a rotary disc 34 fixed to the shaft 17 and carrying an inner circular contact or-ring 35 and two outer oppositely disposedcontacts or segments 36 and 37 (see Figs. 9 to 13). The segmentv 37 has an arcuate length of 180 degrees, while the segment 36' is slightly shorter. These three contacts are secured to the disc 34 by screws 39, and insulated therefrom by mica sheets 40 and 41. The screws 39 extend through insulating bushings 42. The ring 35 and the segment 36 are electrically connected by a conducting strip 43 (Figs. 4 and 9) held at vits ends by'the heads for screwsin electrical contact with these twoparts. f

A vertical bracket 44, xed to the base v6 in front of the commutator 1, has a lateral extension or arm 45 (Fig. 3) 'on which is mounted a` brush-holder 46 carrying a brush 47 engaging with the inner circular contact 35; This brushholder is shown in detail in Fig. 7 and comprises a sleeve 48 extending through an insulating bushing 49 and held in place by the nut 51 jand the the proper circuit conductor between said wash-l ers and tightening the cap 55 thereon.

A brush-holder 56, of similar construction, carries a brush 57 adapted to cooperate with the outer segments 36 and 37. This brush-holder 56 is mounted on a separate plate *or arm 59 (Fig. 3) having a hub portion 60 (Fig. 4) keyed to a sleeve 61 Ajournaled in a bearing on the support 44 coaxially with the shaft 17 This-sleeve 6l also serves as a bearing for the shaft ,17. A worm gear 62 is attached to the outer end of the sleeve 61 and meshes with a worm 64. The latter is formed on one. end of a small shaft 65 journaled on the face of `the bracket 44 and -carrying at its free end a knob 66 by means of which it may be manually rotated to cause a corresponding rotation of the arm 59. This rotation enables an adjustment of the position of the brush 57 in the holder 56 relative to its cooperating contact segmentsl 36 and 37. A y

The low-speed commutator. comprises a disc 67 having mounted thereon a plurality of inner I and outer segments shown in detail in Figs. 9 to 13 inclusive. There are six outer segments numbered 69, 70, 71, 72, 73 and 74 and ive inner segments numbered 75, 76, 77, 78 and 79. These segments are of predetermined arcuate lengths and are positioned relatively to one another in acertain manner as will be further described. They are secured to and insulated from the disc 67 inthe same manner as the high-speed commutator contacts on the disc 34. The outer segment 72 and the inner segment are in electrical connection through a conducting strip 80 andtwo of their respective attaching screws. Three brushes 81, 82 and 83 are' mounted to slidably cooperate with the outer segments and three brushes4 84, 85 and 86 are similarly supported to slidably cooperate with the inner segments.- gAll of these brushes are also positioned relatively to one another and to their cooperating contacts in a certain spectively. These several holders may beof the same construction as previously described and are mounted on a disc 94 in the relation shown.

By referring to Fig. 5 it will be seen that the disc 94 is rotatably mounted on a sleeve 95, which also forms a journal for the shaft 26 and extends into the hub. portion 96 of a yoke shaped bracket 97 (Fig. 2) iixe'd to the base 6. The outer end of the sleeve 95 is threaded and rprojects beyond the hub to which it is clamped by a nut 99.

From the construction shown, it is clear that a rotary displacement of the disc 94 on the sleeve'95 shifts the position of all of the brushes on said disc relatively to their cooperating contact segments on the disc 67. A shaft 100 (Fig. 2) is journaled in the two arms of the bracket -97 and carries at one end a vknurled knob 101 by means of which lit may be manipulated. The

shaft 100 has an intermediate threaded portion 102 (Fig. 6) having mounted thereon an interiorly threaded block 103 carrying a pin 104 engaging in a notch or slot 105 formed in the disc 94. A rotation of the knob 101 will cause displacement of the disc-94 to properly adjust all of the loW-speed'commutator brushes simultaneously.

The wire conductors connected to the holders vof both the high-speed and low-speed commutator brushes and the wire conductors connected tothe terminals of the switch 5 are led to a junction box 106 (Fig. 1), where they are each connected to a corresponding terminal 107. This junction box may be constructed by providing a rectangular opening 109 (Fig. 5) through the base 6 and closing it by a bottom plate 110, of insulating material, carrying the -the act of just leaving said segment.

the terminals 107 of the junction box as may be required to interconnect the various commutator brushes, the switch 5 and the terminals 112 and 113 in the manner illustrated schematically in Figs. 9 to 13.

Referring first to Fig. 9, it will be observed that the binding post 112 is connected by a conductor 114 to the outer brush 57 of the highspeed commutator l. The inner brush 47 of said commutator is connected by a conductor 115 to the outer brush 81 of the low-speed commutator 2. The outer brushes 82 and 83 and the inner brush 84 of the latter commutator are connected to one another by the bridging conductors 116, and therefore the return circuit of all three brushes is completed by the conductor 117 leading to the binding post 113. The inner and outer brushes 47 and 57 of the high-speed commutator are connected respectively by the conductors 119 and 120 to the upper and lower terminals on one side of the switch 5. Corresponding terminals on the other side of said switch are connected respectively by the conductors 121 and 122 to the inner brushes and 86 of the low-speed commutator. As will be later explained, when the switch 5 is open, the two commutators provide a flashing current of one cycle, and when the switch 5 is closed, a hashing current of three cycles.

A (iO-cycle alternating current power source 124 is connected to the input terminals of a switch 125, the output terminals of which are connected by the conductors 126 and 127 to the plug 9. With the switch 125 closed and the plug 9 inserted in the socket 7, current is lsupplied to the motor 4. 4In the embodiment of the invention illustrated, the motor speed is 1800 R. P. M. With the switch 125 closed, current is also supplied by the conductors 129 and 130 to the primary winding 131 of a step-up transformer 132. The secondary winding 134 of this transformer is provided with a suitable number of taps any one of which may be selected by an arm or tap switch 135. The untapped end of the winding 134 is connected v`through a push-button switch 136 to one terminal of the lamp 137 to undergo test. The other terminal of said lamp and the arm 125 are connected respectively to the binding posts 112 and 113. The voltage on the lamp 137 is adjusted to the required value by the transformer tap switch.

Since the high-speed commutator is driven directly by the motor 4, its speed is also 1800 R. P. M. or 30 R. P. S., and since it is in synchronism with the frequency of the power source, the latter will alternate exactly through two complete cycles for each full revolution of this commutator. It is noted that contact is made between the brushes 47' and 57 through the conducting strlp 43 when the brush 57 engages the segment 36, and that this contact is broken when the brush 57 engages the segment 37. Thus, the commutator. 1 is short-circuited during one-half revolution and open-circuited during the other half. Since a period of time corresponding to one cycle elapses when the brush 57 slidingly engages the segment 36, the brush 57 can be so adjusted that the voltage thereon (assuming the switch 136 depressed) is zero, i. e. at a zero point of the wave, when the brush 57 is in the act of just engaging the segment 36 and also when in This adjustment of the brush 57 is assumed in Figs. 9 to 13. Consequently, the high-speed commutator 1 provides a one-cycle contact between the brushes 47 and 57 during each half revolution thereof, this contact occurring when the potential is zero and being broken also when the potential is zero. During the other half revolution contact is broken for a period of time corresponding to one complete cycle of the alternating current wave. In Fig. 9, the cornmutater l is shown in the position when contact is just being broken and the low-speed coininutator 2 is also shown in the position it assumes at that particular instant.

In the embodiment of the invention shown in the drawings, the speed reduction provided by the worm 19 and the gear 27 (Figs. 4 and 5) is 30 to l, i. e. the speed of the low-speed commutaton is 1 R.. P. S. Thus, the low-speed commutator will rotate 6 degrees for each half revolution of the high-speed commutator. In Fig. 9, the outer brush 81 oi the low-speed commutator is just in the act of engaging the outer segment 69, and the outer brush 82 is bearing on said segment. A rotation of the low-speed commutator from vits position shown, although causing contact between the brushes 8l and 82 throughr the segment 69 will not cause current to flow through the lamp 137, since contact has been `broken between the brush 57 and the segment 36. In Fig. 10 the positions of the high-speed aitlowspeed commutators are shown when they have rotated 180 degrees and 6 degrees respectively from their positions in Fig. 9. The brushes 81 and 82 are still engaging the segment 69 and the brush 57 is just contacting with the segment 36. Thus, 4in Fig. 10 (assuming the push button switch l36depressed), the following circuit is established: the winding 134, the switch 136, the lamp 137, the binding post 112, the conductor 114, the high-speed commutator 1, the conductor 115, the low-speed commutator 2, the conductor 117, the binding post 113, the tap switch 135, and back to the winding 134. This circuit is evidently established at a zero point .of the wave.

Assuming the switch 5 open, a flashing current flows through the aforesaid circuit for a period corresponding to one cycle or for 1/60 of a second, as may be understood from inspection of Fig. 11. Here the commutators 1 and. 2 are shown when they have rotated 180 degrees and 6 degrees respectively from their positions shown in Fig. 10. The brush 57 on the high-speed commutator is just leaving the segment 36 and the brush 82 on the low-speed commutator is just leaving the contact 69. Current through the filament is thus broken at that instant (at a zero point of the wave).

A continued rotation of. the commutators will not cause current to flow until the commutators are again in the positions shown in Fig. l0, i. e. until the low-speed commutator will have rotated the remaining portion of one revolution.

With the switch 5 open, the one cycle flashing current willbe consequently repeated for each revolution of the low-speed commutator. Since the speed of the latter is 1 R. P. S., this flashing current recurs each second.

The closing of the switch 5 does not cause flow of current in the filament circuit during the time taken by the commutators 1 and 2 to rotate from their positions of Fig. 9 intotheir positions of Fig. 10, as during this particular period of time, no contact is made between the brushes 47 and 57 and the inner brushes 85 and 86 (in electrical contact through the switch 5 with the brushes 47 and 57 respectively) on the inner segments 78 and 75 of the low-'speed commutator are each open circuited. It is to be noted that during this same periodof time the outer brush 83 of the low-speed commutator is slidably engaging the .outer segment 71 of said commutator. When the two commutators have assumed their positions of Fig. 10, this brush 83A has just made contact with the outer segment 72 in electrical contact through the strip with the inner-segment 75. Thus, in Fig. 10, since the brushes 82 and 83 are electrically connected together, the terminals 112 and 113 are in electrical contact through the brushes 57, 86, 83 and 82, and flow of current through the filament circuit (assuming the switch 136 depressed) is permitted. Also, at that instant, contact is made between the brushes 57 and 47, so that flow of current is also permitted through the brushes 57,' 47, 81 and v82. It is obvious that the ashing current again occurs at a zero point of the wave.

AWhen the two commutators have rotated into the positions shown in Fig. 1l, the brush 57 is just leaving the segment 36 and the brush 82 is just leaving the segment 69 as before explained.v

However, with the switch 5 closed, current is still permitted to fiow through the brushes 57, 86, 83 and 82. Fig. 12 shows the positions of the high-speed and low-speed commutatrs when having rotated respectively 180 degrees and 6 degrees from their positions of Fig. 11. During this rotation, byreason of the shortcircuit provided through the brushes 57, 86, 83 and 82, a second cycle of current is caused to flow through the filament circuit. It is noted that in Fig. 11 the brush 84 is just engaging the inner segment 78, so that, during the rotations of the commutators from their positions of Fig. 11 into their positions of Fig. 12, the brush 84 is slidably engaging the segment '78. vDuring this rotation, since the brushes 84 and 82 are electrically connected together, the brush 47 is in electrical connection with the brush 82 through the conductor 119, the upper side of switch 5, the conductor 121, the brush 85, the segment 78 and the brush 8 4. In Fig. 12, the brush 86 is vjust `leaving the segment 75, so that, upon further rotation, contact will be broken between the brushes 57 and 83 and hence between the brushes 57 and 82.v However, in Fig. 12, contact is ,being made between the brush 57 and thesegment 36 so that, upon, further rotation, the terminals 112 and 113 are short circuited through the brushes 57, 47, 85, 84 and 82 and a third cycle of flashing currentthrough the filament circuit therefore initiated.

Fig. 13 shows the positions of the high-speed and lowspeed commutatore when having rotated 180 degres and 6 degrees respectively from their positions of Fig. 12, or one and one-half revolutions and 18 degrees respectively from their positions of Fig. 10. Here, the brush 485 is just leaving the segment 78. Upon further rotation of the commutators, contact is broken between the brushes 84 and 85, thereby interrupting the current through the filament circuit. No further current will be caused to flow through the lamp 137 until the rotation of the commutators brings them back to their positions shown in Fig. 10. Therefore, with the switch 5 closed, a flashing current of three cycles occurs each time the low-speed commutator revolves one full revolution, i. e. every second.

It is to be particularly noted that since 60 cycles of the current wave occur during each full revolution of the low-speed commutator and only two cycles of the wave occur during each full revolution of the high-speed commutator, and the latter is better adapted to have its brushes adjusted to establish and interrupt the current at zero points of the wave. In other words, the brush 57 can be adjusted with great precision to establish and interrupt the fiashing current at zero points of the wave. Therefore,

the low-speed commutator brushes are so ad- I cause the brush 57 to be just in the act of,

making contact with the segment 36 instead of leaving it in Fig. 9),it could be shown that the i same flashing periods of one cycle and three cycles are obtained with the switch 5v open and closed respectively, and that, by proper adjustment of thebrushes, the flashing currents established and interrupted as before at substantially exactly zero potential.

Means should preferably be provided to Warn the operator of the forthcomingvflash so that he may have his attention directed to the filafiash. In the embodiment of the invention ily ment undergoing test upon occurrence of the lustrated, in view of the short intervals of time I.

at which successive flashes occur, an alarm or click is sounded each time the low-speed commutator assumes its position of Fig. 9, i. e. the alarm occurs at the moment of passage of current through the filament. This gives the operator sufficient time to depressthe key 136 for the succeeding flash. Referring to Figs. 2 and 8, the disc 94 has a slot 1 50 through which extends one arm 151 of a'crank or click 152. The latter is pivotally mounted on a pin 154 xed to the two arms of a bracket 155 secured to said disc. A torsion spring 156 maintains the other arm 157 of the crank, normally in engagement with the bracket 155. The arm 151 is normally in the path of a stud 159 positioned on the lowspeed commutator disc 67, which stud thus causes the arm 157 topivot and impact, when released, periodically with the bracket 155. The stud 159 is so relatively positioned that this impact is caused at the moment of the -flash through the filament undergoing observation.

The switch 136 is convenient in that the' operator may permit the low-speed commutator to rotate through severaly revolutions without current being passed through the filament circuit, this to enable the filament to cool off if it has been unduly heated by successive flashes therethrough. The switch 136 may be maintained continuously depressed when testing small lamps and may be so manipulated, when testing higher current lamps, as to cause the flash to occur less frequently or.recur at any desired interval of time greater than 1 second and a. multiple thereof.

The embodiment of the invention which has been described permits tests to be performed on lamps ranging from small flashlight lamps to high currents lamps of 1000 Watts and more.

It is understood that various modifications of the apparatus illustrated and described herein are possible without departing from the principle of the invention. For example, a single commutator rotating at low speed may be provided, and yet the flashing current interrupted substantially at zero potential. The rotary switching means may 'be so modified as to permit transmitting a flashing current of less than one cycle or anypredetermined portion of the alternating current wave through the filament, and it need not interrupt the flashing current when its instantaneous value is zero. For example, when working with small electric lamps, it may be desired to impress across their lilaments the peak portion of the alternating current Wave.

What is claimed is:

1. The method of detecting a portion or portions of increased resistance in a current-conducting wire comprising passing a current through said wire to permit any resistance increased portion or portions thereon to become lighted and interrupting said current before the entire body of said wire reaches a substantially uniform temperature.

2. The method of detecting a portion or portions of increased resistance on a current-conducting fllament comprising flashing said filament with a current of predetermined strength and predetermined duration to permit any resistance increased portion or portions thereon to become heated to a-temperature of visibility prior to appreciable heating and lighting ofthe remaining portion of said filament.

3. The method of detecting portions of inlcreased resistance on current-conducting wires comprising transmitting through such wire a` current of small duration to permit an increased resistance portion to be rendered visible by the light it produces and repeatedly transmitting such current at regular intervals of time.

4. The method of detecting a portion or portions of increased resistance ona current-conducting fllament comprising passing an alternating current through said filament to permit any increased `resistance portion or portions thereon to become lighted and interrupting said current when-its instantaneous value is zero and before the en tirebody of said filament reaches a substantially uniform temperature.

5. The method of testing lamp filaments to detect spots thereon having an increased resistance comprising passing a predetermined portion of an alternatingcurrent wave through such lllament to permit such spot to be rendered visible by the light it produces..

6: An apparatus for detecting spots in electrical conducting wires, comprising a source of alternating current, a synchronous motor operated thereby, a circuit in which such wire is disposed and derives its'current, a high-speed commutator driven by said motor and brushes therefor for transmitting a flash of current through said circuit, a low-speed commutator also driven by said motor and brushes therefor for periodically transmitting said ash through said circuit, and a switch for manually controlling the current through said circuit 7. An apparatus for detecting portions of increased resistance in electrical conducting wires, an alternating current power supply, a synchronous motor operated from Said supply, a

circuit in which such Wire is disposed and receives its current from said supply, a high-speed commutator driven by said motor and brushes therefor for transmitting a flash of current through said circuit, and a low-speed commutator also driven by said motor and brushes therefor for periodically transmitting said flash through said circuit, said high-speed commutator and brushes therefor interrupting each flash at a zero point of the alternating current wave.

8. An apparatus for detecting portions of increased resistance in electrical conducting wires, comprising a source of alternating current, a synchronous motor, operated from said source, a circuit in which such wire is disposed and receives its current from said source, a high-speed commutator driven by said motor and brushes therefor for transmitting -through said circuit a flashing current consisting of a predetermined portion of the alternating current wave, a lowspeed commutator alsovdriven by said vmotor and brushes therefor for 'periodically transmitting said ilashing current through said circuit, and means for varying said predetermined wave portionto be periodicallytransmitted.

9. An apparatus for detecting portions of increased resistance in electrical-conducting lilaments, comprising an alternating current power supply,` a synchronous motor'operated from said supp1ya circuit for the filament receiving its current from said supply, rotary means driven by the motor for periodically transmitting through said circuit a filament flashing current consisting of one complete cycle of the alternating current wave, further rotary means driven by said motor for periodically transmitting through said circuit a lament flashing current consisting of three complete cycles of the alternating current Wave, and means for rendering one of said rotary means operative in said circuit.

10. An apparatus for detecting portions of increased resistance in electrical conducting Wires, comprising an alternating current power supply, a synchronous motor operated from said supply, a circuit Ifor the wire receiving its current from said supply, a high-speed commutator driven by said motor and brushes therefor for transmitting through said circuit a predetermined portion of the alternating current wave, and a lowspeed commutator driven by said motor and brushes therefor for periodically transmitting through said circuit said predetermined portion of the alternating current wave.

11. An apparatus for detecting portions of increased resistance in electrical conducting wires, comprising an alternating current power supply, a Synchronous motor operated from said supply,

, a circuit for the wire receiving its current from said supply, high-speed commutating means driven by said motor and brushes therefor for transmitting through said circuit a predetermined portion of the alternating current wave, low-speed commutating means driven by said motor and brushes therefor for periodically transmitting through said circuit said predetermined portion, further low-speed commutating means driven by said motor and brushes therefor for increasing the length of said predetermined portion, and means for rendering operaytive `in said circuit one of said low-speed ccmmutating means and brushes.

HOLD H. Mmmm. ROBERT PASH. 

